Dihydronaphthalene production



United States Patent 3 278 620 DIHYDRONAPHTl-EAI JENE PRODUCTION Lynn H. Slaugh, Pleasant Hill, Calif., assignor t0 Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed May 29, 1964, Ser. No. 371,178 9 Claims. (Cl. 260-667) This invention relates to an improved method for the partial hydrogenation of naphthalene. More particularly it relates to an improved method for the production of dihydronaph-thalene.

Numerous methods are available in the art for the hydrogenation of naphthalene. Customary products of catalytic hydrogenation processes are tetralin and/or decalin, i.e., compounds wherein any unsaturation present in the rings remains aromatic in character or alternatively the rings are completely saturated. Greater difficulty is attendant to processes of partial hydrogenation, that is, processes wherein one or both rings retain carbon-carbon unsaturation that is not aromatic in character. A typical partial hydrogenation process involves the reaction of naphthalene with alkali metal in liquid ammonia in the presence of water or other hydroxylic compound. In such cases, the alkali metal is converted to compounds, e.g., the hydroxide or alkoxide, from which the alkali metal is not readily recoverable. The inherent expense of such processes has precluded their usage on any large scale basis. It would be of advantage to provide a more economical method for the production of partially hydrogenated naphthalene.

It is an object of the present invention to provide an improved processes for the partial hydrogenation of naphthalene. More particularly, it is an object to provide an improved process for the production of dihydronaphthalene.

It has now been found that these objects are accomplished by the process of contacting naphthalene with alkali metal and molecular hydrogen in inert solvent. In the process of the invention, dihydronaphthalene is obtained in good yields, and the alkali metal is recoverable in a chemically combined form from which the alkali metal is easily regenerated.

In the process of the invention, the naphthalene is contacted in liquid-phase solution in inert solvent with alkali metal and molecular hydrogen. The term alkali metal is employed herein to indicate a member of Group I of the Periodic Table, e.g., lithium, sodium, potassium, rubidium or cesium or to indicate mixtures, e.g., alloys, of two or more of such metals. Although lithium is operable as the alkali metal in the process of the invention, it is generally preferred to utilize more active alkali metal, that is, alkali metal having an atomic number from 11 to 55, particularly when a single alkali metal is to be employed. From the economic considerations the use of sodium or potassium or alloys thereof is most suitable. Particularly satisfactory results are obtained with sodium-potassium alloys containing from about 20% to about 80% by weight of sodium.

The alkali metal is preferably employed in amounts equivalent to or in excess over the naphthalene. Probable stoichiometric considerations for the reaction require 2 gram-atoms of alkali metal for each moles of naphthalene, and although ratios of gram-atoms of alkali metal to mole of naphthalene from about 1:1 to about 8:1 are satisfactory, ratios from about 2:1 to about 6:1 are preferred.

The solvent employed in the process of the invention is an inert, non-hydrogenatable solvent which is capable of dissolving the naphthalene reactant. Preferred solvents are polar solvents, that is, contain uneven charge distribution within the solvent molecule. Illustrative of suitable solvents are the aliphatic ethers having up to 12 carbon atoms, and containing only C, H and O atoms, including acylic mono-ethers such as diethyl ether, dibutyl ether, methyl hexyl ether, isopropyl heptyl ether, butyl octyl ether and ethyl amyl ether; lower alkyl ethers (full) of polyhydric alcohols wherein the alkyl moieties have from 1 to 4 carbon atoms, e.g., dimethoxyethane, glycerol tributyl ether, propylene glycol diethyl ether and 1,2,6-tripropoxyhexane; lower alkyl ethers of poly(oxyalkylene) glycols such as diethylene glycol dimethyl ether and tetraethylene glycol diethyl ether; and cyclic ethers such as tetrahydro'furan, tetrahydropyran, 2,4-dimethyltetrahydrofuran, 1,3-dioxolane, 2,2-dimethyldioxolane, 1,3-dioxane, 1,4-dioxane, and 2,2-diethyl-1,3-dioxane; as well as aliphatic tertiary amine solvents having up to 12 carbon atoms and containing only C, H and N atoms, such as triethylamine, trihexylamine, methylethylpropylamine, dibutylethylamine, amyldiisopropylamine and dimethyloctylamine. It is also within the contemplated scope of the process to employ solvents containing both ether and tertiary amine moieties, e.g., triethan-olamine trimethyl ether. In general, the ether solvents are a preferred class of solvents, especially the cyclic ethers.

The process of the invention comprises contacting the naphthalene with the alkali metal and molecular hydrogen. Without wishing to be bound by any particular theory, it appears likely that the alkali-metal reacts with the naphthalene to produce a mono-metal adduct, e.g., a naphthalene free-radical ion, which subsequently reacts with hydrogen to produce the dihydronaphthalene product and the alkali metal hydride. The process is therefore adaptable for a one-step or a two-step operation. A typical two-step process comprises reacting the naphthalene in the inert solvent with alkali metal to form the naphthalene-metal reaction product, and subsequently introducing molecular hydrogen to produce the desired dihydronaphthalene. In an alternate modification of the process, the solution containing naphthalene is simultaneously contacted with alkali metal and molecular hydrogen to efiect the partial hydrogenation in one step.

The process of the invention is typically conducted in an autoclave or similar pressure reactor. As the alkali metal is not soluble in the reaction solvent and the process is therefore heterogeneous in character, it is desirable to provide some means for agitation of the reaction mixture as by shaking or stirring. The partial hydrogenation is conducted at any convenient temperature so long as the reaction mixture is maintained in the liquid phase. Temperatures from about 10 C. to about 130 C. are generally satisfactory, although temperatures from about 0' C. to about 110 C. are preferred. Best results are obtained when a hydrogen pressure that is greater than atomspheric is employed. The optimum hydrogen pressure Will in part depend upon the reaction temperature that is employed, and the hydrogen pressure can, of course, vary during the reaction as hydrogen is consumed. For convenience, the suitable hydrogen pressures are characterized in terms of the maximum hydrogen pressure attained during reaction. Hydrogen pressures from about p.s.i.g. to about 1500 p.s.i.g. are satisfactory, although pressures from about 300 p.s.i.g. to about 1000 p.s.i.g. are preferred.

Subsequent to reaction, the product mixture is separated from the insoluble alkali metal hydride by conventional means, as by distillation, filtration or the like, and the alkali metal is subsequently recovered from the hydride as by known methods of pyrolysis.

The dihydronaphthalene product comprises a mixture of isomeric 1,2-dihydronaphthalene and 1,4-dihydronaphthalene which are separable from each other as well as from other components of the product mixture by such methods as fractional distillation or chromatographic techniques.

The dihydronaphthalene products are useful as chemical intermediates. The ethylenic linkage serves as a reactive site for co-polymerization with reactive monomers, or alternatively may be epoxidized to form useful epoxy resin precursors. The ethylenic linkage is cleaved by mild oxidation to form di basic acids from which useful conventional derivatives including polyesters and .polyamides are prepared, or serves as a dienophile in reaction with many dienes. Additionally, the ethylenic linkage is hydrated or hydroxylated to form alcohols from which other useful derivatives are prepared.

To further illustrate the improved process of the invention, the following examples are provided. It should be understood that the details thereof are not to be regarded as limitations, as the teachings thereof may be varied as will be understood by one skilled in this art.

Example I.-To an autoclave was charged 20 millimoles of naphthalene, 80 milligram-atoms of sodium metal and 150 ml. of tetrahydrofuran. The reactor was pressurized with hydrogen and maintained at 106 C. for 1 hour, during which time the maximum hydrogen pressure was 850 p.s.i.g. At the conclusion of reaction when hydrogen uptake had ceased, the product mixture was nearly colorless and contained insoluble sodium hydride. The entire product mixture was solvolyzed by the addition of water and the organic products were determined by gas-liquid chromatography. Based upon the 62.7% yield of volatile products, the yield of 1,2-dihydronaphthalene was 22.8%

Example Il.-To an autoclave was charged 20 millimoles of naphthalene, 69 milligram-atoms of a sodiumpotassium alloy containing approximately 76.7% by weight potassium and 150 ml. of tetrahydrofuran. The reactor was charged with hydrogen and maintained at about 8 C. for two hours. The maximum hydrogen pressure was 400 p.s.i.g. The entire product mixture, comprising a colorless solution and a precipitate of metal hydride, was solvolyzed with water and the organic products of the resulting mixture were determined by gasliquid chromatography. Based upon the 68.6% yield of volatile products, the yield of 1,2-dihydronaphthalene was 26.9% and the yield of 1,4-dihydronaphthalene was 31.9%.

Example III.-To an autoclave was charged 20 millimoles of naphthalene, 62.6 milligram-atoms of a sodiumpotassium alloy containing approximately 76.6% by Weight potassium and 150 ml. of tetrahydrofuran and the mixture was stirred for 3 hours at room temperature. Hydrogen was then introduced and the mixture maintained at about 20 C. for 0.5 hour. The maximum hydrogen pressure was 440 p.s.i.g. The product mixture was solvolyzed with water and the organic products were determined by gas-liquid chromatography. Based upon the 87.5% yield of volatile reaction products, the yield of 1,2- dihydronaphthalene was 36.8% and the yield of 1,4-dihydronaphthalene was 41.8%.

Similar results are obtained when 1,2-dimethoxyethane is employed as solvent. Good results are also obtained when triethylamine is employed as the solvent.

Example IV.-The procedure of Example I was followed to react 2O millimoles of naphthalene with milligram-atoms of lithium metal in 200 ml. of tetrahydrofuran at a temperature of 110 C. for 1.1 hour at a maximum hydrogen pressure of 830 p.s.i.g. The product mixture was found to contain both 1,2- and 1,4-dihydronaphthalene. In this experiment, the solvolysis was conducted using heavy water, i.e., deuterium oxide. The gas evolved during solvolysis was found to consist principally of HD, thus evidencing the prior hydrogenation of the naphthalene and the concomitant formation of lithium hydride, and little or no deuterium was found in the organic products.

I claim as my invention:

1. The process for the production of dihydronaphthalene by contacting naphthalene, dissolved in an inert, nonhydrogenatable solvent, under liquid phase conditions with alkali metal and molecular hydrogen, at a temperature from about 10 C. to about 130 C.

2. The process for the production of dihydronaphthalene by contacting naphthalene, dissolved in an inert, nonhydrogenatable ether solvent, under liquid phase conditions with alkali metal having an atomic number from 11 to 55, and molecular hydrogen, at a temperature from about 10 C. to about 130 C.

3. The process of claim 2 wherein the ether is 1,2-dimethoxyethane.

4. The process of claim 2 wherein the ether is diethylene glycol diethyl ether.

5. The process for the production of dihydronaphthalene by contacting naphthalene, dissolved in an inert, nonhydrogenatable cyclic ether solvent, under liquid phase conditions with alkali metal having an atomic number from 11 to 55, the ratio of gram-atoms of said alkali metal to moles of said naphthalene being from about 1:1 to about 8:1, and molecular hydrogen, at a temperature of from about 0 C. to about C.

6. The process of claim 5 wherein the alkali metal is sodium.

7. The process of claim 5 wherein the alkali metal is sodium-potassium alloy containing from about 20% to about 80% by weight of sodium.

8. The process of claim 5 wherein the ether is tetrahydrofuran.

9. The process of claim 5 wherein the ether is 1,4 dioxane.

References Cited by the Examiner UNITED STATES PATENTS 2,021,567 11/1935 Muckenfuss 260-667 2,929,854 3/1960 Wilson 260-667 2,968,681 1/1961 OConner et al 260-667 3,122,593 2/ 1964 Wilson et al. 260-667 DELBERT E. GANTZ, Primary Examiner. SAMUEL P. I ONES, Assistant Examiner. 

1. THE PROCESS FOR THE PRODUCTION OF DIHYYDRONAPHTHALENE BY CONTACTING NAPHTHALENE DISSOLVED IN AN INERT, NONHYDROGENATABLE SOLVENT, UNDER LIQUID PHASE CONDITIONS WITH ALKALI METAL AND MOLECULAR HYDROGEN, AT A TEMPERATU5E FROM ABOUT-10*C. TO ABOUT 130*C. 